Hyun Chan Kim

Cellulose long fibers fabricated from cellulose nanofibers and its strong and tough characteristics

Cellulose nanofiber (CNF) with high crystallinity has great mechanical stiffness and strength. However, its length is too short to be used for fibers of environmentally friendly structural composites. This paper presents a fabrication process of cellulose long fiber from CNF suspension by spinning, stretching and drying. Isolation of CNF from the hardwood pulp is done by using (2, 2, 6, 6-tetramethylpiperidine-1-yl) oxidanyl (TEMPO) oxidation. The effect of spinning speed and stretching ratio on mechanical properties of the fabricated fibers are investigated. The modulus of the fabricated fibers increases with the spinning speed as well as the stretching ratio because of the orientation of CNFs. The fabricated long fiber exhibits the maximum tensile modulus of 23.9 GPa with the maximum tensile strength of 383.3 MPa. Moreover, the fabricated long fiber exhibits high strain at break, which indicates high toughness. The results indicate that strong and tough cellulose long fiber can be produced by using ionic crosslinking, controlling spinning speed, stretching and drying.

Calcinated tea and cellulose composite films and its dielectric and lead adsorption properties.

In this paper, calcinated tea and cellulose composite (CTCC) films were fabricated via solution casting method. Chemical structure, morphology, crystallinity and thermal stability of the fabricated films were characterized by using Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. The effect of calcinated tea loading on the properties of the prepared CTCC films was studied. The results suggest that the prepared CTCC films show higher mechanical properties, thermal stability and dielectric constant than the neat cellulose film. In addition, the CTCC films adsorb Pb2+ ions and its adsorption performance depends on the calcinated tea content and pH level. The CTCC films are useful for sensors, flexible capacitor as well as lead adsorption applications.

Flexible cellulose and ZnO hybrid nanocomposite and its UV sensing characteristics

Abstract This paper reports the synthesis and UV sensing characteristics of a cellulose and ZnO hybrid nanocomposite (CEZOHN) prepared by exploiting the synergetic effects of ZnO functionality and the renewability of cellulose. Vertically aligned ZnO nanorods were grown well on a flexible cellulose film by direct ZnO seeding and hydrothermal growing processes. The ZnO nanorods have the wurtzite structure and an aspect ratio of 9 ~ 11. Photoresponse of the prepared CEZOHN was evaluated by measuring photocurrent under UV illumination. CEZOHN shows bi-directional, linear and fast photoresponse as a function of UV intensity. Electrode materials, light sources, repeatability, durability and flexibility of the prepared CEZOHN were tested and the photocurrent generation mechanism is discussed. The silver nanowire coating used for electrodes on CEZOHN is compatible with a transparent UV sensor. The prepared CEZOHN is flexible, transparent and biocompatible, and hence can be used for flexible and wearable UV sensors.

MWCNT Coated Free-Standing Carbon Fiber Fabric for Enhanced Performance in EMI Shielding with a Higher Absolute EMI SE

A series of multi-walled carbon nanotube (MWCNT) coated carbon fabrics was fabricated using a facile dip coating process, and their performance in electrical conductivity, thermal stability, tensile strength, electromagnetic interference (EMI) and shielding effectiveness (SE) was investigated. A solution of MWCNT oxide and sodium dodecyl sulfate (SDS) in water was used in the coating process. MWCNTs were observed to coat the surfaces of carbon fibers and to fill the pores in the carbon fabric. Electrical conductivity of the composites was 16.42 S cm−1. An EMI shielding effectiveness of 37 dB at 2 GHz was achieved with a single layer of C/C composites, whereas the double layers resulted in 68 dB EMI SE at 2.7 GHz. Fabricated composites had a specific SE of 486.54 dB cm3 g−1 and an absolute SE of approximately 35,000 dB cm2 g−1. According to the above results, MWCNT coated C/C composites have the potential to be used in advanced shielding applications such as aerospace and auto mobile electronic devices.

Transparent and semi-interpenetrating network P(vinyl alcohol)- P(Acrylic acid) hydrogels: pH responsive and electroactive application

ABSTRACT In this paper, poly(vinyl alcohol)-poly(acrylic acid) based transparent semi-interpenetrating network (semi-IPN) hydrogels were synthesized by using a solvent mixture of dimethyl sulfoxide and deionized water via free radical polymerization and subsequent freeze-thaw technique. The formation of the semi-IPN hydrogels was conformed from FT-IR spectra. The acrylic acid concentration effect on the hydrogels was investigated in terms of transparency, crystalline structure and thermal stability by using UV-visible spectroscopy, X-ray diffraction and thermogravimetric analysis. Swelling behaviours of the semi-IPNPAP hydrogels were studied in deionized water and different pH solutions. The compression and electroactive behaviour was tested in fully hydrated stage by using compression test and by applying electrical voltage. The hydrogels showed displacements under the applying voltage and detailed experiment is illustrated.

Green all-cellulose nanocomposites made with cellulose nanofibers reinforced in dissolved cellulose matrix without heat treatment

Green all-cellulose nanocomposites were fabricated by adding reinforcing cellulose nanofiber (CNF) to a matrix of dissolved cellulose. CNFs were isolated from one dried native hardwood bleached Kraft pulp and office waste recycled deinked copy/printing paper (DIP) by using the TEMPO oxidation method. The cellulose was dissolved by using DIP and DMAc/LiCl solvent without heat treatment and solvent exchange to form a matrix of the all-cellulose nanocomposites. The DIP was not only selected for CNF isolation, but also for the cellulose matrix. The isolated CNFs and the all-cellulose nanocomposites were characterized by atomic force microscopy, thermogravimetry–differential thermal analysis, X-ray diffraction and mechanical tensile testing. The green all-cellulose nanocomposites made without heat treatment offered better thermal stability, crystallinity and mechanical properties than the heat treated ones. CNFs isolated from two resources show similar reinforcement capacity in all-cellulose nanocomposites. All-cellulose nanocomposite fabrication by dissolving cellulose without heat treatment and solvent exchange is a simple way that saves energy and chemicals.

Ultrasonic wave propagation of flexible piezoelectric polymer for tactile actuator: simulation and experiment

This study deals with ultrasonic wave propagation on a piezoelectric polymer substrate for tactile actuator. On the piezoelectric polymer substrate, a pair of interdigital transductor (IDT) electrodes is patterned by lift-off process and a resonator is made by exciting the IDTs. A standing wave is generated between the pair of IDT electrodes, of which the wavelength matches with the distance between two IDTs. The standing ultrasonic waves can give different textures to the users. The wave propagation in this periodic structure on the polymer substrate is studied by harmonic and transient analysis. Vertical displacement and induced voltage at the output IDT electrode are calculated and the ultrasonic wave generation is experimentally verified. The proposed concept of tactile actuator based on ultrasonic wave is explained.

Miniaturized 3???3 array film vibrotactile actuator made with cellulose acetate for virtual reality simulators

This paper reports an array vibrotactile actuator which is suitable for fitting into virtual reality simulators. A 3 × 3 array actuator, of size 15 × 15 × 1 mm3, consists of nine cantilever structured cells of which the pillars are supported and made with cellulose acetate by a molding technique. The fabrication process and performance test along with results for the suggested vibrotactile actuator are explained. To simulate the touch force, the top mass is added on the actuator and the actuator performance is measured under actuation. When 2000 Vp–p voltage is applied to the actuator, the averaged maximum acceleration for all cells is 0.44 ± 0.19 g, which is above the vibrotactile threshold. The actuation mechanism is associated with the electrostatic force between top and bottom electrodes.

Array haptic actuator for flight simulator

Array haptic actuator to realize texture of button for virtue flight simulator is fabricated by using cellulose acetate (CA) film. The haptic actuator has independent 3 × 3 cells for identical vibration. Each cell consists of topside CA layer and bottomside CA layer with two pillars. Two ends of topside CA layer are fixed on the pillars similar with fixed end beam. By an electrostatic force in the presence of electric field, the topside CA layer vibrates. Each cell shows its resonance frequency peak in the capable frequency range of vibrotactile feeling from 100 Hz to 500 Hz. The acceleration performance is shown to be higher than vibrotactile threshold on wide frequency band from 100 Hz to 400 Hz.

Graphene oxide–gellan gum–sodium alginate nanocomposites: synthesis, characterization, and mechanical behavior

This paper reports the preparation and characterization of graphene oxide–gellan gum–sodium alginate nanocomposites (GO–GG–Alg). The nanocomposites were prepared by a simple solution mixing-evaporation method. Fourier transform infrared spectroscopy, X-ray diffractions, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, and mechanical testing were conducted to study the structure and properties of the nanocomposites. The obtained findings reveal that gellan gum, sodium alginate, and graphene oxide are able to form a homogeneous mixture. Small amount of GO loading on GO–GG–Alg drastically improves its tensile strength and Young’s modulus. Detailed material characteristics of the nanocomposites are addressed.